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  • Science Project: need help with watts

    Hello
    I am doing a College Science project on Solar Energy and I would like to know if any one has a way of measuring the amount of DC current coming from the panels?
    Thanks!
    Nathaniel

  • #2
    Something like this works well. How much current do you want to measure? There may be less expensive alternatives.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      You could use the DC Amps function of a simple multimeter if its max current rating is more than expected from the panels. Or, passing the panel current through a current shunt will let you use a DC voltmeter (such as a simple multimeter) to to measure currents that are much larger than the meter's built-in current function is capable of. See here for a good description of current shunts used in this way. It's about halfway down the page.

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      • #4
        If you are trying to measure the current when it is not connected to anything, set your multimeter to amps (you may need to move the leads) and measure across the plus and minus. If you are trying to measure while they are connected, interrupt the negative wire and put the multimeter leads in line with the negative, putting the meter in series with the circuit.

        If your multimeter doesn't have a DC Amp feature, there are some inexpensive digital DC amp meters on Amazon.
        Solar Queen
        altE Store

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        • #5
          Originally posted by Amy@altE View Post
          If you are trying to measure the current when it is not connected to anything, set your multimeter to amps (you may need to move the leads) and measure across the plus and minus. If you are trying to measure while they are connected, interrupt the negative wire and put the multimeter leads in line with the negative, putting the meter in series with the circuit.

          If your multimeter doesn't have a DC Amp feature, there are some inexpensive digital DC amp meters on Amazon.
          Be careful of those low cost multimeter's because they might have very low amp ratings and it is easy to blow the fuse inside the meter.

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          • #6
            Originally posted by SunEagle View Post
            Be careful of those low cost multimeter's because they might have very low amp ratings and it is easy to blow the fuse inside the meter.
            True, I was assuming from the subject of science project that it was a small array. Bad assumption.
            Solar Queen
            altE Store

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            • #7
              It's funny how many different ways we can come up with to say the same thing.

              Edit: I'm wondering if he really means "power" since it's in his subject line.

              Nathaniel, you can calculate the power produced by the panel by measuring the voltage across the panel + and - with a voltmeter, and multiplying that by current in the panel wires as described above. For example, 12.5V x 5.6 Amps = 70 Watts.

              If you're using a charge controller that "chops" the panel DC on and off to regulate charge to a battery, such as a PWM controller, use a "True RMS" meter for both voltage and current.

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              • #8
                Originally posted by sdold View Post
                It's funny how many different ways we can come up with to say the same thing.

                Edit: I'm wondering if he really means "power" since it's in his subject line.

                Nathaniel, you can calculate the power produced by the panel by measuring the voltage across the panel + and - with a voltmeter, and multiplying that by current in the panel wires as described above. For example, 12.5V x 5.6 Amps = 70 Watts.

                If you're using a charge controller that "chops" the panel DC on and off to regulate charge to a battery, such as a PWM controller, use a "True RMS" meter for both voltage and current.
                Well, almost. The above method will give you about 130% of real power, the Isc is higher than your amps at max power, and the Voc is higher than volts at max power. If your panel has a sticker that lists Ipmax and Vpmax you can multiply those 2 numbers together and get an accurate nameplate power for the panel.
                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

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                • #9
                  Originally posted by Mike90250 View Post
                  Well, almost. The above method will give you about 130% of real power, the Isc is higher than your amps at max power, and the Voc is higher than volts at max power. If your panel has a sticker that lists Ipmax and Vpmax you can multiply those 2 numbers together and get an accurate nameplate power for the panel.
                  True, I assumed he would be making the measurements while the panel was operating.
                  Last edited by sdold; 02-03-2015, 07:16 PM. Reason: Less wordy

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